Effects of Mouthwashes on the Oral Microbiome and Systemic Health

Effects of Mouthwashes on the Oral Microbiome and Systemic Health

OVERVIEW

While antimicrobial mouthwashes are proven to be clinically effective for management of certain oral microbial diseases, recent studies suggest tha, in addition to targeting bacteria responsible for gum diseases such as gingivitis and periodontitis, they may harm healthy bacteria and disturb the balance and protective role of the oral microbiome (dysbiosis).

Most findings on the oral microbiome and mouthwashes involve chlorhexidine use, demonstrating that it may induce dysbiosis and compromise the host oral microenvironment . A recent study completed in 2025 has shown that CPC mouthwash can also inhibit nitrate synthesis in the mouth. However there remains a need for further research on other agents used in mouthrinses, such as hydrogen peroxide, essential oils, to determine whether their clinical effectiveness in managing oral disease is accompanied by changes to the oral microbiome. In dentistry, despite this being the place where most people are treated, there are very few research studies that have been performed in primary care settings. Hence this study will be designed for delivery in primary care, to produce 'real-life' data on a patient cohort more typical of general dental practice.

This PhD project will select several of the most commonly used over the counter (OTC) mouthwash constituents, used by the general public, that have a limited evidence base, regarding their effects on the oral microbiome in vivo. . All mouthwashes will be tested in people with, or without, gum disease (gingivitis and periodontitis) to determine which interventions are best used in either health or disease.

PROJECT AIMS

The aim of this project is to determine the role of different mouthwashes on the oral microbiome and its relationship with cardiovascular health. We will achieve this by conducting a double-blinded randomised clinical trial (pilot study) in a primary care dental setting, to investigate (i) the composition of the oral microbiome in different oral niches in periodontal health and disease, and (ii) determine how the oral microbiome is altered by the use of different mouthwashes during oral health and disease, with either , essential oil (EOs), CPCs, hydrogen peroxide (H2O2); all versus placebo (water or saline).

OVERVIEW

While antimicrobial mouthwashes are proven to be clinically effective for management of certain oral microbial diseases, recent studies suggest that, in addition to targeting bacteria responsible for gum diseases such as gingivitis and periodontitis, they may harm healthy bacteria and disturb the balance and protective role of the oral microbiome (dysbiosis).

• Inclusion & Exclusion

All individuals aged 18 years and older will be eligible to take part in this study. Exclusion will apply to individuals who:

Are current smokers, due to the well-documented impact of smoking on oral and systemic health.

Have a known diagnosis of hypertension, diabetes, or cancer, as these systemic conditions may influence oral microbiome and inflammatory responses.

Have taken a course of antibiotics within the last three months, since antibiotics are known to disrupt microbial balance and may confound the interpretation of oral microbiome data.

Report allergies to essential oils or to milk proteins, as these ingredients may be present in the study mouthwash and could trigger adverse reactions.

In addition, participants who have never previously used a mouthwash will be excluded. This is a precautionary measure designed to avoid even the minimal possibility of adverse responses.